This invention relates to a method and an apparatus for transforming voluminous material, particularly textile fibres, by pressing the material into bales.
With known baling presses the bales are packed and bound in a press. A usual procedure is to attach a planar sheet to the surfaces of the press die and press table before the final pressing operation takes place. After the final pressing is completed, the sheets are folded over the long sides of the bale. The short sides are covered with loose sheets, which sheets are attached by sewing to the remaining packing. Typically, two compression-molded hoods are attached to the press die and press table prior to the final pressing operation and then are heeled manually over the completely pressed bale. This can be carried out after the mold covers have been opened. Laminated polyethylene fabric is usually used as a packing material.
The pressed and packed bales then are bound at full pressing effect with metal wires or strips, which are cut to suitable lengths and provided with eyes or stampings for securely hooking them together. Each bale normally is bound with seven wires of 3 mm diameter or strips of 16 mm by 0.5 mm cross-section. In the lastmentioned case the cross-sectional area per strip is 8 mm.sup.2. At a rated tensile strength of 100 kg per mm.sup.2 the strips together can thus withstand an expansion force in the completed bale of 7.times.2.times.8.times.100=11,200 kg. Textile fibre material, however, is very expansive, which requires final compressing of the bale to a height substantially below the final bale height in order not to exceed the limiting force value of 11,200 kg. This requirement often results in compression forces of up to 250,000 kg corresponding to a specific pressure of 50 kg per cm.sup.2 on a bale with a mold area of 5000 cm.sup.2. After the ensuing expansion of the bale the corresponding area is about 5800 cm.sup.2 and, consequently, the permissible maximum specific expansion pressure is 11,200 kg per 5800 cm.sup.2, i.e. about 3 kg per cm.sup.2. It should be apparent from the aforesaid that both the packing and binding with known arrangements is a complicated and expensive procedure. The work must be carried out manually in the press. A simpler method of packing and binding at a place other than in the press, under similar conditions as in the press, involves serious difficulties. The transport of the bale while maintaining a pressing force of 250,000 kg would imply very great forces, and the fibre easily would be damaged by friction heat.
An object of the present invention is to overcome the aforesaid shortcomings by providing a method and apparatus wherein the bale, after the final pressing in a pressing chamber, is permitted to expand in the press at a pressing effect substantially lower than the final pressing effect, whereafter the bale without the occurance of detrimental friction forces is moved out of the pressing chamber to a binding device while the aforesaid substantially lower pressing effect is maintained. The binding is carried out with tension in the binding wires or strips so that the completed bale does not appreciably expand after the removal of the pressing effect.